Object-Oriented Programming Notes and Tasks

An object has attributes and methods.

Attribute: a dot-accessible label on an object that points to a piece of data
Method: a function or procedure attached to a class that operates on an instance of the class
Class: a data structure consisting of attributes, and (optionally) methods

class Monster
    private poisonous
    private strength
    private name

    public procedure new(given_poisonous, given_strength, given_name)
        poisonous = given_poisonous
        strength = given_strength
        name = given_name
    endprocedure

    public procedure eat()
        print(name + " eats a hero. Mmmmmm, delicious!")
    endprocedure

    public procedure sleep()
        print("Snore, snore, snore")
    endprocedure

    public procedure greet(person)
        print("Hello " + person + ". I am " + name + "!")
    endprocedure
endclass

Attributes for type Monster: poisonous, strength, name
Methods for type Monster: eat, sleep, greet (new is not a method, but an initialiser)

Instantiation: where an object is created of a given type, with a set of values for its attributes

The initialiser (new in the OCR pseudocode) is used to instantiate a new object.

MonsterThree = new Monster(false, 4.5, "Susie")

MonsterThree.sleep()

Snore, snore, snore

Inheritance: where one class of object gets all the methods and attributes of its parent classes
Overriding: where one class with methods inherited from its parent class redefines a method defined on its parent

vampireTwo = new Vampire(false, 8.5, "Gordon")

class Goblin inherits Monster
    private gold_coins = 0

    public procedure new(given_gold_coins, given, given_strength, given_name)
        gold_coins = given_gold_coins
        super.new(false, given_strength, given_name)
    endprocedure

    public function get_gold_coins()
        return gold_coins
    endfunction

    public procedure eat()
        print(name + " eats a hero loudly. CHOMP CHOMP CHOMP!")
    endprocedure
endclass

Polymorphism: the ability to call a method of an object and have it do different things depending on the type of the object

for monster of zoo
    monster.greet("Computer Science Students")
endfor

Encapsulation: the limitation of attribute access to within an instance's own methods only

class Monster
    private poisonous
    private strength
    private name
    ...

    public procedure set_strength(entered_strength)
        if strength < 1 || strength > 20
            return
        endfor
        strength = entered_strength
    endprocedure
endclass